Photodiodes comprise a plurality of electrode radiation-sensitive junctions formed in semiconductor material. Within a photodiode, charge carriers are created by light that illuminates the junction and reverse current is generated that varies with illumination. Photodiodes are used for detection of optical power and subsequent conversion of the same to electrical power. Operationally, photodiodes absorb charged particles, which facilitate detection of incident optical power, thereby generating current proportional to the incident power.
Photodiodes are typified by the quantification of certain characteristics, such as electrical, optical, current (I), voltage (V), and noise. Electrical characteristics predominantly include shunt resistance, series resistance, junction capacitance, rise or fall time and frequency response whereas optical characteristics include responsivity, quantum efficiency, non-uniformity, and non-linearity. Noise in photodiodes is generated by a plurality of sources including, but not limited to, thermal noise, quantum or photon or shot noise, and flicker noise.
In the semiconductor industry it is often desirable to increase light-induced current of photodiodes in order to increase the signal-to-noise ratio and thereby enhance photodiode sensitivity. Photodiode sensitivity is crucial in low light-level applications and is typically quantified by noise equivalent power (NEP) defined as the optical power that produces a signal-to-noise ratio of unity at the detector output. NEP is usually specified at a given wavelength and over a frequency bandwidth of 1 Hz and is therefore expressed in units of W/Hz1/2.
Silicon photodiodes, essentially active solid-state semiconductor devices, are among the most popular photodetectors coalescing high performance over a wide wavelength range with unmatched user-friendliness. For example, silicon photodiodes are sensitive to light in the wide spectral range, approximately 200*10−9 m to 1200*10−9 m, extending from deep ultraviolet all the way through visible to near infrared. Additionally, silicon photodiodes detect the presence or absence of minute light intensities thereby facilitating extremely precise measurement of the same on appropriate calibration. For instance, appropriately calibrated silicon photodiodes detect and measure light intensities varying over a wide range, from very minute light intensities of below 10−13 watts/cm2 to high intensities above 10−3 watts/cm2.
Silicon photodiodes can be employed in an assortment of applications including, but not limited to, spectroscopy, distance and speed measurement, laser ranging, laser guided missiles, laser alignment and control systems, optical free air communication, optical radar, radiation detection, optical position encoding, film processing, flame monitoring, scintillator read out, environmental applications such as spectral monitoring of earth ozone layer and pollution monitoring, low light-level imaging, such as night photography, nuclear medical imaging, photon medical imaging, and multi-slice computer tomography (CT) imaging, and thin wafer applications.
Nonetheless, numerous problems exist with existing photodiodes. Specifically, generating thin wafer photodiodes in which leakage current and noise is controlled but the wafer is sufficiently sturdy to handle processing and use is difficult. Popular applications including, but not limited to, computer tomography (CT), utilize thin wafer photodiode arrays produced on large diameter wafers. The production of such arrays is often plagued by excessive loss due to breakage of the delicate thin wafers.
Various approaches have been made in the prior art to manufacture semiconductor devices on large diameter wafers. Japan Patent Application No. JP-A 2004200305 titled “METHOD OF MANUFACTURING SOI WAFER HAVING DIAMETER OF SIX INCHES OR MORE” to Takahashi Yoshiki et al. uncovers a method by which an SOI wafer, the whole diameter of which can be used as a device forming area, and can be manufactured without increasing the manufacturing cost nor lowering the productivity.
U.S. Pat. No. 6,537,418 titled “Spatially uniform gas supply and pump configuration for large wafer diameters” to Muller, K. Paul et al. by and large relates to semiconductor wafer etching and more specifically to an improved gas distribution plate which substantially reduces the non-uniformities in the etch process that occurs across the semiconductor wafer.
Europe Patent Application No. EP-A 1308000544 titled “SILICON SINGLE CRYSTAL WAFER HAVING VOID DENUDED ZONE ON THE SURFACE AND DIAMETER OF ABOVE 300 mm AND ITS PRODUCTION METHOD” to IIDA, M. et al. relates to a silicon single crystal wafer having a diameter of 300 mm or more and a defect-free layer and a method for producing the same.
The prior art fails to provide a thin wafer photodiode structure and method of manufacturing that produces sufficiently sturdy wafers while still maintaining the overall performance characteristics of photodiode arrays and their individual diode units, within detection systems.
Consequently, there is still a need for economically, technically, and operationally feasible methods, apparatuses, and systems for manufacturing thin wafer photodiode arrays. More exclusively, there is demand for cost-effective computer tomography (CT) scanner photodiode array while still maintaining the overall performance characteristics of the photodiode array and individual diode units.